Method, medium, and system for searching crossover router and method, medium, and system for reserving resources in mobile network

ABSTRACT

A method, medium, and system for reserving resources in a mobile network. A mobile node reports a start of a handover to a present access router if the handover of the mobile node occurs, and the previous access router transmits specified session information to a candidate access router that has a possibility handling the mobile node&#39;s handover. A candidate crossover router, which performs a resource reservation work on a new path and a resource release on the previous path, is searched, and a localized resource reservation is established by exchanging a specified resource reservation message before the handover is completed if the candidate crossover router is determined. Accordingly, duplication of resources can be prevented, and a prompt resource reservation can be achieved during the handover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/968,364filed Oct. 20, 2004 which claims priority benefit under 35 U.S.C. § 119from Korean Patent Application Nos. 10-2003-0073177, filed on Oct. 20,2003, and 10-2004-0002472, filed on Jan. 13, 2004, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method, medium, andapparatus for reserving resources when a handover occurs in a mobilenetwork. More particularly, the present invention pertains to a method,medium, and apparatus for reserving resources by searching for acandidate access router and a candidate crossover router for an areawhere a mobile node will potentially move, and pre-reserve or re-reservethe appropriate resources through a router found through the search.

2. Description of the Related Art

As information and globalization ages draw near, research into activewireless Internet systems has increased. Wireless Internet can bebriefly classified into fixed wireless Internet and mobile wirelessInternet. Fixed wireless Internet is limited in mobility, but hassuperior transmission capacity and speed. Systems for WLAN (WirelessLocal Area Network), B-WLL (Broadband Wireless Local Loop), LMDS (LocalMultipoint Distribution Service), and Bluetooth, belong to the wirelessfixed Internet. By contrast, the mobile wireless Internet, which isimplemented by different types of systems in notebook computers and PCs,according to the generations of the mobile communication network,secures the mobility superiority, but is limited in transmissioncapacity and speed.

With the development of mobile communication networks, the mobilewireless Internet has developed from an initial form, such as CDPD(Cellular Digital Packet Data) using the 1st generation AMPS (AdvancedMobile Phone Service) network, to a service form using wirelessapplication protocols such as WAP (Wireless Application Protocol), ME(Mobile Explorer) and I-mode, based on the 2nd or 2.5-generationIS-95/GSM network. The standardization of ALL IP mobile networks basedon IMT-2000, which is the 3rd-generation mobile communication system,has progressed in stages, and it is expected that the IP-basedstandardization will be gradually carried out from the fields ofIP-based core networks to wireless access networks and terminals.

The present ALL IP mobile network is the next-generation mobilecommunication network which has become a matter of great concern allover the world, with standardization work having progressed in the 3GPP(3rd Generation Partnership Project) around Northern Europe and in the3GPP2 (3rd Generation Partnership Project 2) around North America. Fromthese projects, many technical issues have been brought to light in theacademic world, through various kinds of forums and through thestandardization and development of the ALL IP mobile network carried outthrough various kinds of consortiums made up by world-famous mobilecommunication network providers, manufacturers developing networkconstituent elements, Internet service providers providing new Internetservices, and manufacturers of IP packet network constituent elements.

In order to support the mobility in the mobile wireless network wherethe ALL IP is implemented, an MIP (Mobile IP) and a QoS (Quality ofService), securing a reliable transmission of data and multimediatraffic, are required. The reliable transmission of the multimediatraffic is supported by a pre-reservation of network resources, forwhich an RSVP (Resource Reservation Protocol) has been mainly used.However, since the present RSVP was not designed to take intoconsideration the mobility of wireless networks, a proper resourcereservation cannot be made when MIP is implemented.

After the appearance of MIP, research for a resource reservation formobile networks has continuously progressed, and the representativeprotocols are MRSVP (Mobile RSVP), RSVP-MP (RSVP Mobility Proxy), andCORP (method of Concatenation and Optimization for resource ReservationPath).

FIG. 1 illustrates paths for pre-establishing resources, according tothe conventional MRSVP. MRSVP classifies resource reservation statesinto a passive reservation state and an active reservation state. Thepassive reservation state is a state where a resource has beenpreviously reserved, and not presently in use, and the activereservation state is a state where the reserved resource is in use. Aproxy agent is provided in an access router to manage the transmissionof a user's mobile terminal or mobile node 10 from the passivereservation state to the active reservation state. The mobile node canmove within a mobile network and accordingly changes its network accessposition. The proxy agent manages cells adjacent to a cell where themobile node is positioned, and preemptively takes part in a multicastRSVP session through special reservation schemes, wherein traffic is notactually transferred.

Referring to FIG. 1, the mobile node 10 establishes a communicationsession with a correspondent node 20 through a path 1. The correspondentnode 20 communicates with the mobile node 10 by connecting with theaccess router CAR included in a core network.

In this state, if a handover of the mobile node 10 occurs, the mobilenode 10 transmits a specification message to adjacent access routersAR2, AR3, . . . , and ARn. The specification message includes a flowspecification, which is to be transmitted to a remote proxy agent by themobile node and a flow ID (Identification). Between the access routersAR2, AR3, . . . , and ARn, where a communication session is notcurrently established, and the correspondent node 20, the passivereservation state is set. If the mobile node 10 moves, it can extend thereservation path by changing a corresponding passive reservation stateto an active reservation state and by transferring traffic through theactive reservation state.

Although this solved the problem of time delay of the QoSre-establishment, MRSVP pre-reserves resources of adjacent cells wherethe mobile terminal may move in the mobile network, which may be shortof resources, thereby wasting resources in the access network. Themobile node should keep a mobility specification that includes positioninformation for all of the neighbors of the mobile node while the mobilenode moves and as it establishes a communication session with thecorrespondent node 20. Since an intermediate router manages all stateinformation about passive reservation states, unnecessary overheadoccurs, which emphasizes a corresponding problem of the mobile networkhaving limited scalability. When the mobile node 10 moves, communicationsessions between mobile node 10 and previous resources in a previouscell are not promptly released, thereby creating a double reservationbeing kept with respect to the same communication session, causing awaste of resources. As these handovers frequently occur, generating suchdouble resource reservations, the resource availability of newcommunication sessions becomes disturbed.

FIG. 2 illustrates paths for establishing new resources through anaddress changing method, according to the conventional RSVP-MP. TheRSVP-MP structure is mutually combined with hierarchical mobilitymanagement schemes of MIP, is provided with an RSVP-MP agent placed atMAP (Mobility Anchor Point) or in GFA (Gateway Foreign Agent), andperforms an address change between an LCoA (Local Care-of-Address),which is an address of the access router, and an RCoA (RegionalCare-of-Address), which is a global address of another address.

Referring to FIG. 2, the mobile node 10 establishes a communicationsession with a correspondent node 20 through path 1. If the mobile node10 performs a handover from an area managed by AR1, which is currentlyconnected to the mobile node 10, to an area managed by AR2, mobility 10is allocated with CoA, a new temporary address, and requests are-establishment of resource reservation according to the change ofpaths. If an end-to-end re-establishment of resources from the mobilenode 10 to the correspondent node 20 is made, the resourcere-establishment creates a time delay, preventing the mobile node 10from being properly provided with QoS.

However, if the handover of the mobile terminal 10 occurs, the RSVP-MPstructure performs communication by converting LCoA of the accessnetwork into RCoA that is a global address through an MP (MobilityProxy) and using RCoA. Thus, according to the RSVP-MP structure,re-establishment of entire paths is not required, but only requires thepath in a section between AR1 and MAP, in which LCoA is used, to bere-established. That is, RCoA is used from MAP to the correspondent node20, and thus, even if a handover occurs, it is not required tore-establish the RSVP session from MAP to the correspondent node, butonly requires the RSVP session to be re-established between the mobilenode to MAP. Since RSVP-MP does not require the re-establishment of theend-to-end resource reservation, it can reduce time delays due to thelimited required re-establishment of the RSVP-MP session.

Although RSVP-MP does not require the reestablishment of the end-to-endresource reservation, a time delay of as much as one round-trip timestill occurs in order to establish the resource reservation, and aprompt release of the reservation state of the resources establishedthrough the old access router is not performed, thereby similarly againcausing the double reservation of resources. If the handover frequentlyoccurs, the handover still disturbs the resource use for newcommunication sessions due to the double resource maintenance. Since theRSVP-MP structure should be implemented in parallel to the hierarchicalmobility management schemes of MIP, which have not yet been completed,it cannot be an independent protocol and, accordingly, may be changed asit is implemented.

FIG. 3 is a view illustrating a conventional CORP type RSVP pathextending process through a hierarchical reservation path and pathextending process using an optimized reservation path.

Referring to FIG. 3, the CORP type RSVP provides QoS by using a methodof extending the existing RSVP path if a handover occurs. The CORP typeRSVP uses a CRP (Concatenation for Reservation Path)r to extend the RSVPpath.

The CRP type RSVP extends the RSVP path using PRPs (Pseudo ReservationPaths). The CRP type RSVP determines one representative BS (BaseStation) among BSs (Base Stations) managed by one access router, andpre-reserves the resources for adjacent BSs.

Referring to FIG. 3, several access routers AR1, AR2, . . . , ARn, whichbelong to the access network, manage respective areas area 1 to area n.Each respective area includes several cells, and a BS manages therespective cells. If the mobile node 10 performs a handover in the areamanaged by one access router, the BS that manages the cell that themobile node 10 accordingly has reached, transmits a CRP informationmessage (that is, information message) for informing BSs, of theadjacent cells, of the arrival of the mobile node at BSs, and makes theadjacent cells pre-reserve their resources.

The continuous extension of the RSVP path by CRP makes an infinite pathor a loop path, and in order to prevent this, an ORP (Optimization forReservation Path) is used along with CORP. Specifically, if a handoveroccurs within an area managed by one access router AR1, the handover isprocessed according to CRP, while if a handover occurs due to the mobilenode's movement to another access router AR2, the mobile node 10establishes a new RSVP session with the correspondent node 20.Accordingly, in the case of the handover occurring in one access router,resources can be promptly secured, and thus previous problems caused bythe path extension can be solved with QoS being secured.

As described above, since CORP pre-reserves the resources of adjacentcells to which the mobile node will move and simultaneously establishesthe end-to-end RSVP session in a mobile network having insufficientresources, the inefficient waste of resources occurs in the accessnetwork. Since CORP uses a multicast method when establishing a newsession by extending the path, and since there should also be a new RSVPsession established from a new access router to the correspondent node20 whenever the mobile node moves to another access router, troubleoccurs in scalability of the network. Although CORP releases oldresources, unlike MRSVP, the release of the existing resources accordingto CORP includes the release of the existing resources up to thecorrespondent node 20, and thus a prompt process is not achieved and anew session establishments for other terminals are disturbed.

SUMMARY OF THE INVENTION

Embodiments of the present invention have been developed in order tosolve the above drawbacks and other problems associated with theconventional arrangement. An aspect of the present invention is toprovide a method, medium, and an apparatus for reserving resources whichcan promptly determine a candidate access router and a candidatecrossover router and pre-reserve or re-reserve appropriate resourcesusing refresh bits when a handover occurs.

The present invention can be applied to a mobile network that includes amobile node, a correspondent node communicating with the mobile nodethrough a specified network, a first access router for making the mobilenode access the specified network, a second access router for handingover the mobile node, and a crossover router for establishing a new paththrough the second access router.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

To achieve the above and/or other aspects and advantages, embodiments ofthe present invention provide a method for searching for a crossoverrouter in a mobile network having a mobile node, a correspondent nodecommunicating with the mobile node through a specified network, a firstaccess router enabling the mobile node to access the specified network,a second access router accepting the mobile node after being handed overfrom the first access router, and a crossover router for establishing anew path through the second access router, including the second accessrouter transmitting a message including specified session information toan adjacent router positioned in a direction of the correspondent nodeon the new path, the adjacent router comparing a session ID included inthe received message with a currently reserved session ID, comparing alogical interface number through which the message is received with apre-stored logical interface number if the session Id and the reservedsession ID are identical, and recognizing the adjacent router as thecrossover router when it is confirmed from the received message that ahandover of the mobile node occurs, if the pre-stored logical interfacenumber and the logical interface number are not identical.

The adjacent router may compare a flow ID included in the message withan existing flow ID if the pre-stored logical interface number and thelogical interface number are identical, and recognize the adjacentrouter as the crossover router when it is confirmed from the receivedmessage that the handover of the mobile node occurs, if the existingflow ID and the message flow ID are not identical. The adjacent routercomparing of the session ID may include the adjacent router transmittingthe message to a router in the direction of the correspondent node ifthe message session ID and the currently reserved session ID are notidentical.

The method may include a confirming of whether the adjacent router,which is recognized as the crossover router, can perform a communicationnormal operation with the mobile node and the correspondent node, and asearching for another crossover router among adjacent routers on the newpath formed through a routing protocol if it is confirmed that theadjacent router is in a failure state and cannot perform the normalcommunication operation.

The confirming of whether the adjacent router can perform the normaloperation may include an old router of the crossover router on the newpath transmitting a specified search message to the crossover router,and a recognizing that the crossover router is in the failure state if aconfirmation message of the specified search message is not received ina specified time from the crossover router. The recognizing that thecrossover router is in the failure state may further include atransmitting the confirmation message, from the crossover router, with acookie of specified contents, and the old router confirming whether theconfirmation message is an effective message may be performed bychecking the cookie.

To achieve the above and/or other aspects and advantages, embodiments ofthe present invention may include a method for reserving resources in amobile network having a mobile node, a correspondent node communicatingwith the mobile node through a specified network, and a first accessrouter enabling the mobile node to access the specified network,including the mobile node reporting a start of a handover to the firstaccess router if the handover of the mobile node occurs, the firstaccess router transmitting specified session information to a candidateaccess router which has a possibility of handling the mobile node'shandover after searching for the candidate access router, searching fora candidate crossover router to perform a resource reservation on a paththrough the candidate access router and a resource release on a paththrough the first access router, and establishing a localized resourcereservation by exchanging a specified resource reservation message witha found candidate access router before the handover is completed.

The specified session information may include a session IDdiscriminating between respective sessions, a flow ID discriminatingbetween respective data flows, and a mobility object indicating amobility of the mobile node. In addition, the header portion of thespecified resource reservation message may contain specified refreshbits, such that by setting a specified bit value within the refresh bitsindicating a pre-reservation of resources and a reservation limit timefor refreshing a state of a pre-reservation of resources.

The method may further include refreshing the resource reservation withthe candidate access router if a resource pre-reservation state is heldlonger than the reservation limit time. Further, the searching for thecandidate crossover router may include the candidate access routertransmitting a specified message containing the specified sessioninformation to an adjacent router positioned in a direction of thecorrespondent node on the path, the adjacent router confirming whethermessages having the same session ID are input through different logicalinterfaces, determining whether the handover occurs by confirming themobility object if the messages having the same session ID are inputthrough the different logical interfaces, and recognizing the adjacentrouter as the candidate crossover router if it is determined that thehandover occurs.

The searching for the candidate crossover router further includescomparing a flow ID of a received message with an existing flow ID ifthe messages having the same session ID are input through the samelogical interface, determining whether the handover occurs by confirmingthe mobility object if the flow ID of the received message and theexisting flow ID are identical, and recognizing the adjacent router asthe candidate crossover router if it is confirmed that the handoveroccurs.

The establishing of the localized resource reservation may include thecandidate crossover router recognizing a resource pre-reservation stateby confirming the refresh bits in a receiver-initiated type resourcereservation, transmitting the reservation message corresponding to apath message if a sender between the candidate crossover router and thecandidate access router transmits the path message to the receiver, andthe sender, which has received the reservation message, establishing theresource pre-reservation by transmitting a confirmation message to thereceiver. Further, the establishing of the localized resourcereservation may include the candidate crossover router recognizing aresource pre-reservation state by confirming the refresh bits in asender-initiated type resource reservation, and establishing theresource pre-reservation by transmitting a confirmation messagecorresponding to the reservation message if a sender between thecandidate crossover router and the candidate access router transmits thereservation message to a receiver.

The candidate crossover router may establish the localized resourcereservation with the candidate access router by not transmitting amessage for the resource reservation received from the candidate accessrouter in the direction of the correspondent node based on the candidatecrossover router review of the refresh bits.

In addition, the method may include the mobile node completing ahandover to a second access router among candidate access routers, themobile node transmitting a binding update message to a crossover routerestablishing a path through the second access router among the candidatecrossover routers, and the crossover router releasing the resourcereservation established on the existing path by transmitting a resourcerelease message teardown message to the first access router. The methodmay further include completing a handover to a second access routeramong candidate access routers in a state that a resourcepre-reservation is not established, and the crossover router, whichestablishes a path through the second access router among the candidatecrossover routers, establishing the localized resource reservation.

Refresh bits, of a header portion of the specified resource reservationmessage, may include a mobility bit setting a resource reservationbetween the crossover router and the second access router and a resourcereservation refresh limit time. The crossover router establishing of thelocalized resource reservation may include a router positioned on a pathbetween the candidate crossover router and the candidate access routermaintaining a path state where information about an existing path isstored before the handover is terminated, the crossover router and thesecond access router exchanging a resource establishment messageincluding a mobility bit, if the mobile node performs the handover tothe second access router, and the crossover router establishing thelocalized resource reservation by recognizing the mobility bit.

The method may include the crossover router releasing existing resourcesestablished with the first access router if the localized resourcereservation is established, refreshing a resource reservation state onthe path including the second access router if the resource reservationstate is held longer than the refresh time set by the mobility bit. Thecrossover router establishing of the localized resource reservationincludes the crossover router establishing the path state bytransmitting a path message in a direction of the mobile node if thecrossover router is a sender in a receiver-initiated type resourcereservation, the mobile node transmitting a binding update message tothe second access router if the mobile node completes the handover tothe second access router, the second access router transmitting the pathmessage to the mobile node, the mobile node transmitting a reservationmessage corresponding to the path message through the second accessrouter, and the crossover router establishing the localized resourcereservation by transmitting a confirmation message corresponding to thereservation message to the second access router.

The crossover router establishing of the localized resource reservationmay included a router positioned on a path between the crossover routerand the second access router storing the information about the existingpath in a sender-initiated type resource reservation, the second accessrouter transmitting a reservation message, in which a mobility bit isset, to the crossover router if the handover is terminated and a bindingupdate message is received, and the crossover router establishing thelocalized resource reservation by transmitting a confirmation messagecorresponding to the reservation message to the second access router.

To achieve the above and/or other aspects and advantages, embodiments ofthe present invention include a system for reserving resources in amobile network, including a mobile node for performing communicationswith a correspondent node through a specified network, a first accessrouter enabling the mobile node to access the specified network andsearching for a candidate access router having a possibility ofperforming communication between the mobile node and the correspondentnode if the mobile node were to move in a mobile node handover, and acandidate crossover router for establishing a localized resourcereservation by exchanging a specified resource reservation message withthe candidate access router before the mobile node's handover isterminated.

The resource reservation message may include a header portion thatcontains specified refresh bits containing time information forrefreshing a resource pre-reservation. The candidate crossover routermay establish a localized resource reservation only with the candidateaccess router, without transmitting the resource reservation message toan upper router in a direction of the correspondent node, if theresource reservation message is received and a resource pre-reservationis confirmed from the refresh bits.

If the mobile node completes the handover to a second access routeramong candidate access routers, a crossover router, which establishes apath through the second access router among the candidate crossoverrouters, releases resources established on an existing path bytransmitting a resource release teardown message to the first accessrouter. If the handover is terminated in a state that the resourcepre-reservation is not established, the crossover router establishes alocalized resource reservation with the second access router.

In addition, refresh bits, of the resource reservation message headerportion, include a mobility bit that contains resource reservationrefresh time information for refreshing the resource reservation betweenthe crossover router and the second access router. If the second accessrouter receives a binding update message from the mobile node in a statethat a resource pre-reservation is not established, the second accessrouter sets the mobility bit in the resource reservation message andtransmits the resource reservation message to the crossover router. Ifthe mobility bit is identified after the resource reservation message isreceived, the crossover router establishes a localized resourcereservation only with the second access router without transmitting theresource reservation message to the upper router.

In a receiver-initiated type resource reservation, the crossover router,if it is a sender, establishes a localized resource reservation byestablishing a path state by transmitting a path message in a directionof the mobile node, and transmitting a confirmation messagecorresponding to the reservation message to the mobile node if thereservation message is transmitted from the second access router after ahandover is completed.

If a binding update message is transmitted from the mobile node in astate that the path state is established, the second access routerimmediately transmits the path message to the mobile node, and if thereservation message is received from the mobile node, the second accessrouter transmits the reservation message to the crossover router. If theresource reservation is re-established, the crossover router releasesexisting resources on a path established between the crossover routerand the first access router by transmitting a teardown message to thefirst access router.

In addition, in the sender-initiated type resource reservation, thesecond access router may transmit the reservation message, in which themobility bit is set, to the crossover router, and the crossover routerreestablishes a localized resource reservation by transmitting aconfirmation message corresponding to the reservation message to themobile node. If the resource reservation is re-established, thecrossover router releases the existing resources on a path establishedbetween the crossover router and the first access router by transmittinga teardown message to the first access router.

To achieve the above and/or other aspects and advantages, embodiments ofthe present invention included a mobile network having a plurality ofaccess routers for communicating between a mobile node and acorrespondent node, through at least one of the plurality of accessrouters by implementing method embodiments of the present invention.

To achieve the above and/or still other aspects and advantages,embodiments of the present invention included a mobile network, having aplurality of access routers for communicating between a mobile node anda correspondent node, through at least one of the plurality of accessrouters, and a system of reserving resources in the mobile network,according to embodiments of the present invention.

Lastly, to achieve the above and/or other aspects and advantages,embodiments of the present invention include a medium having computerreadable code implementing embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 illustrates paths for preemptively establishing resources,according to the conventional MRSVP;

FIG. 2 illustrates paths for preemptively establishing new resourcesthrough an address changing method, according to the conventionalRSVP-MP;

FIG. 3 illustrates a conventional CORP type RSVP path extending process,through a hierarchical reservation path and path extending process usingan optimized reservation path;

FIG. 4 illustrates a resource reservation process in a resourcereservation system, according to an exemplary embodiment of the presentinvention;

FIG. 5 illustrates a process of releasing the existing resource when aresource reservation of a new path is performed in the resourcereservation system, according to an exemplary embodiment of the presentinvention;

FIG. 6 illustrates an upper router's process of recognizing itself as acrossover router in the resource reservation system, according to anexemplary embodiment of the present invention;

FIG. 7 illustrates a header structure of a resource reservation messagefor performing a resource pre-reservation and re-reservation in aresource reservation system, according to an exemplary embodiment of thepresent invention;

FIG. 8 illustrates a flowchart of a crossover router searching method,according to an exemplary embodiment of the present invention;

FIG. 9 illustrates a flowchart of a method of performing a resourcepre-reservation and re-reservation, according to an exemplary embodimentof the present invention;

FIG. 10 illustrates a QoS signaling operation for a resourcepre-reservation during a handover in the resource reservation system,according to an exemplary embodiment of the present invention; and

FIG. 11 illustrates a QoS signaling operation for a resourcere-reservation, when the resource pre-reservation is not made during ahandover in the resource reservation system, according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

Accordingly, the matters defined below, such as a detailed constructionand elements, are nothing but the examples provided to assist in acomprehensive understanding of the invention. Thus, it is apparent thatembodiments of the present invention can be carried out without thosedefined matters. Also, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

FIG. 4 illustrates a wireless mobile network applying a resourcereservation system, according to an exemplary embodiment of the presentinvention. Referring to FIG. 4, this resource reservation systemincludes a mobile node 10, an access router AR1 for enabling the mobilenode 10 to access an access network, several candidate access routersAR2 to AR4, and several crossover routers CR1 and CR2. Accordingly, themobile node accesses a core network through a gateway GW, and in thesame manner, is connected to a correspondent node 20 connected to thecore network using a correspondent access router.

In the resource reservation system, the mobile node 10 and thecorrespondent node 20 basically exchange signaling messages such as apath message, a reservation message, a confirmation message, a rejectionmessage, a teardown message, and an error message, in order to reserveresources required for communications.

The path message is transmitted to a receiver from a sender in order toset a path state, and the reservation message is transmitted so as toreserve the resources in an opposite direction to a direction in whichthe path message is transmitted. The confirmation message is transmittedwhen the resource reservation has been successfully made, and therejection message is transmitted when the resource reservation has notbeen successfully made. The teardown message is used to releasecurrently reserved resources, and the error message is used to reportall errors occurring during the resource reservation.

If an end-to-end resource reservation is made, a reserved session isbasically divided into three types: a correspondent node-crossoverrouter (CN-CR), a crossover router-access router (CR-AR), and an accessrouter-mobile node (AR-MN). The CN-CR section refers to a common path orjoined path where no signaling is changed, and the CR-AR section refersto a part where a localized session change is performed due to ahandover of the mobile node 10.

According to an exemplary embodiment of the present invention, whenperforming the handover, the mobile node instructs a resourcepre-reservation by searching a candidate access router to which themobile terminal possibly will move and a candidate crossover routerprovided when the mobile terminal performs the handover to the candidateaccess router and then generating refresh bits utilizing a field that isnot used in a header portion of the signaling message. If the handoveris completed in a state that the resource pre-reservation is not made,the mobile terminal makes a resource re-reservation made promptly. Therefresh bits are used as an identifier for localization of the resourcereservation.

As shown in FIG. 4, if the mobile node 10 performs a handover from anarea managed by AR1 to an area managed by another access router, ittransmits a handover start message for informing AR1 of a handoverstart. The handover start message may include a mobility specificationthat contains mobility information of the mobile node and information onan adjacent access router. The mobile node 10 determines the handoverstart time point by checking whether the intensity of a signaltransmitted from the present access router AR1 is lowered less than athreshold value, or whether the intensity of a signal transmittedthrough another access router is heightened more than a specified value.The mobile node may report the occurrence of the handover by setting an‘H’ bit in a mobility object to ‘1’ after defining the mobility objectin the path message (when the mobile node is a sender) that is theresource reservation message for refreshing the resource reservation, orthe reservation message (when the mobile node is a receiver).

If the access router AR1 recognizes the start of the handover throughthe handover start message or the refresh message, the access router AR1finds at least one candidate access router AR2 to AR4 by searchingrouters of areas to which the mobile node 10 possibly could move, amongthe adjacent routers. In order to find the candidate access router, aCARD (Candidate Access Router Discovery) algorithm is used. A system(Draft-ieff-seamoby-card-protocol-04.txt) proposed by IETF Seamoby WG orother systems may be used.

If the candidate access router is found through the CARD algorithm, theold access router AR1 transmits session information (e.g., informationsuch as path message information, reservation message information, andmobility specification information) stored in the access router itselfto the appropriate candidate access routers AR2 to AR4. This sessioninformation includes a session ID, flow ID and mobility object thatindicates the mobility of the mobile node 10.

If the candidate access routers AR2 to AR4 are searched, the respectivecandidate access routers search the corresponding crossover routers CR1and CR2 using the session information. If the mobile node 10 performs ahandover from the old access router to a new access router, the upperrouters, positioned on paths in a direction of the correspondent node 20in the old access router and the new access router, will become thecrossover routers. A path is established through the new access router,and the reserved resources, which are not used in the respective routerson the established paths, are released for the old access router.

Accordingly, the crossover routers are changed depending on where themobile node 10 moves. Specifically, the crossover routers may be changedaccording to the candidate access routers AR2 to AR4, and the crossoverrouters corresponding to the candidate access routers are thenconsidered the candidate crossover routers. Referring to FIG. 4, thecrossover router corresponding to AR2 and AR3, among the candidateaccess routers AR2 to AR4, becomes CR1, and the crossover routercorresponding to AR4 becomes CR2. Accordingly, before the completion ofthe handover, CR1 and CR2 become the candidate crossover routers. If themobile node 10 performs a handover to AR3 among the candidate accessrouters, CR1 becomes the crossover router.

The implementation of the above-described candidate crossover routersCR1 and CR2 solve the problem of the double resource reservationoccurring when the end-to-end resource reservation is made and makes aprompt resource reservation possible. Specifically, if a handover of themobile node 10 to one of the candidate access routers AR2 to AR4 occurs,a localized path change occurs only between the candidate access routersand the crossover routers through the crossover routers' identificationof the refresh bits of the path message or reservation message, therebypreventing the double resource reservation by reserving resources forthe routers on the path. By pre-reserving the paths through thecandidate access routers and the candidate crossover routers, a promptresource reservation becomes possible during the handover.

As shown in FIG. 4, in the case of the handover of the mobile nodeaccessing AR1, the mobile node should release the path between AR1 andCR1, and search for a path through another access router. A mergingpoint is provided at the point where the old path connecting through AR1and the new path connecting through the present access router meettogether. Generally, an upper router that serves as the merging pointbecomes the crossover router CR. The crossover router serves to reserveresources through the new path on which the handover occurred, and thenpromptly release resources set on the old path.

A set reservation session has an inherent session ID, and this sessionID can be used to identify the session until the session is terminated.In other words, even if the handover occurs and the path is changed, thesession ID of the reservation session does not change. A data flow thatrequires the resource reservation has one flow ID. This flow ID isconstructed using an IP address of the mobile node 10, an IP address ofthe correspondent node 20, and a port number.

According to an exemplary embodiment of the present invention, acrossover router can be searched using the session ID, flow ID, IPlogical interface (or logical interface number), and mobility object.The candidate access routers AR2 to AR4 transmit the path message orcrossover router (CR) search message to the adjacent routers on thepaths in the direction of the correspondent node 20. That is, if themobile node 10 is the sender, the mobile node 10 transmits the pathmessage, and thus the candidate access routers search the candidatecrossover routers corresponding to the respective candidate accessrouters using the path message. If the correspondent node 20 is thesender, the candidate access routers separately transmit messages forsearching the crossover routers. By setting the ‘H’ bit of the mobilityobject in the message to ‘1’, the candidate access routers may indicatethat the handover of the mobile node has occurred.

An adjacent router, which receives the message, determines whether thesession ID of the currently reserved session is identical with thesession ID of the received path message or the CR search message bycomparing them with each other. If they are not identical with eachother, the adjacent router determines that the session is not reservedin the router, and retransmits the received message to the adjacentrouter in the direction of the correspondent node 20.

If it is determined that the session IDs are identical with each other,the adjacent router confirms the logical interface number of the IPlogical interface through which the path message or CR message isreceived. If it is confirmed that the same session ID is input throughthe different incoming interfaces or logical interface numbers, theadjacent router recognizes itself as the candidate crossover router.

FIG. 5 illustrates a router that receives messages from two differentrouters. As shown in FIG. 5, the messages received from the respectiverouters are input through different logical interfaces (or differentlogical interface numbers), and thus have different IP logical interfacenumbers. Accordingly, if the session IDs included in the respectivemessages are identical with each other, the corresponding router maygenerally be considered the crossover router.

In FIG. 5, if the messages having the identical session ID are receivedthrough different logical interfaces, that is, if the router is therouter CR1 positioned at the merging point of the path formed throughthe new access router AR3 and the path formed through the old accessrouter AR1, the router CR1 may generally be the crossover router.However, if the corresponding router cannot support the RSVP andspecified resource reservation system, it cannot be used as thecandidate crossover router.

The router CR1 positioned at the merging point transmits the sessioninformation in the direction of the correspondent node 20, and theadjacent router CR2 that has received the session information determineswhether the router CR2 itself is the crossover router. Since thecrossover router CR2 is positioned on the joined path, its IP logicalinterface number becomes identical with that of the router CR1.Accordingly, the method as illustrated in FIG. 5 cannot recognize thecrossover router. The flow IDs are compared with each other in order toconfirm whether they are identical with each other. This is because adifferent flow ID is used when the access router is changed due to thehandover. Also, the crossover router may be identified using the logicalinterface number. It is required for the respective nodes to recognizetheir logical interface numbers.

If it is confirmed that the flow ID has changed, the router confirms themobility object of the message. That is, if the ‘H’ bit of the mobilityobject is set to ‘1’, the router confirms the occurrence of the handoverof the mobile node, for which the resource reservation has been made.Accordingly, the upper router CR1 or CR2 determines itself to be thecrossover router, and performs a prompt resource re-reservation andrelease of the existing resources. If the mobile node 10 is the sender,the upper router CR1 or CR2 transfers the received path message to theupper router existing in the direction of the correspondent node on thecommon path to update the resource reservation state. By resetting the‘H’ bit of the mobility object of the path message to ‘0’, the upperrouter prevents the mis-recognition of itself as the crossover router.Whether or not a crossover router has been found, may be indicatedwithout using the ‘H’ bit. In this case, a separate flag bit is used. Inother words, the ‘H’ bit may be used only for indicating a start of ahandover, and the separate flag bit may be separately provided toindicate whether the crossover router has been found or not. Since themobile node 10, which is the receiver, transmits the CR search message,it does not transmit the CR search message to the upper router any moreif the crossover router is determined. The mobility object may include amobility event counter bit. This bit is helpful to the resourcereservation signaling system when a macro mobility or ping-pong typehandover occurs. Specifically, this bit enables the mobile node 10 tocount the number of handover occurrences so that the mobile node canconfirm the final resource reservation message. For example, if ahandover of the mobile node 10 to AR3 occurs before the resourcereservation for AR2 and the resource release for AR1 due to the promptmovement of mobile node 10, which accesses the access network throughAR1 shown in FIG. 4 and moves to AR2 and then to AR3, the crossoverrouter senses the number of handover occurrences by confirming themobility event counter bit of the mobility object, and thus candisregard the resource reservation message produced during the previoushandover.

Although the crossover router can be searched, as described above, thecrossover router should be re-searched when the crossover router failsimmediately after it is found, and thus the resource re-reservation andthe release of the existing resources cannot be performed. It isnecessary to confirm whether the present crossover router is dead oralive. This process is called a DPD (Dead Peer Discovery).

According to DPD, if a router transmits a PD (Peer Discovery) searchmessage to an adjacent router (that is, peer router) on the signalingpath and receives a confirmation message to the PD search message, thestate of the router that takes part in the reservation session of aspecified flow can be confirmed. The node that transmits the PD searchmessage is called a PD requester, and the node that transmits theconfirmation message is called a PD responder. The old router of thecrossover router, which was determined to be the crossover router butcannot perform the crossover function due to the router failure,transmits the PD search message to the crossover router of an adjacentnode. If no confirmation message is received within a predeterminedtime, it is considered that the crossover router is in a dead state, anda new path is formed by the routing protocol, and then a peer router issearched for on the path. If a new peer router is found, the new peerrouter performs the prompt resource reservation and the release of theexisting resources by re-searching the crossover router as describedabove.

The crossover router may include a cookie in the PD confirmation messagefor security and transfers the PD response message including the cookieto the PD requester. The PD requester confirms whether the PD responsemessage is effective by checking the cookie in the PD response message.

If the failure occurs after the crossover router has been found, and theresource reservation and the release of the existing resources has beenperformed, an old hop router, which exists on the new signaling path,becomes the PD requester and performs the DPD process to search for thenew peer router. Since the resource reservation on the old path hasalready been released and the new resource reservation has normally beenmade on the new path, it is not required to re-search the crossoverrouter.

If the candidate crossover routers CR1 and CR2, corresponding to therespective candidate access routers AR2 to AR4, are determined in theabove-described manner, the localized resource reservation is madebetween the respective access routers and the candidate crossoverrouters before the handover is terminated. If the handover is terminatedin a state where the resource reservation has not been made, thelocalized resource reservation is promptly made.

In order to make a resource reservation, the router which has recognizeditself as the candidate crossover router should inform the mobile node10 that the crossover router has been found. If the mobile node 10 isthe sender, the candidate crossover router may report the discovery ofthe crossover router to the mobile node 10 by transmitting a CR-foundpacket, having a small size, to the mobile node 10. If the mobile node10 is the receiver, the correspondent node 20 may report the discoveryof the crossover router to the mobile node 10 by adjusting a specifiedbit value of the transmitted path message.

If the mobile node 10 recognizes the discovery of the crossover routers,corresponding to the respective candidate access routers AR2 to AR4, themobile node 10 takes part in the resource reservation process.Specifically, if the handover is in process, the mobile node 10pre-reserves resources between the respective candidate access routersand the respective candidate crossover routers, and if the handover iscompleted in a state where the resource pre-reservation has not beenmade, the mobile node 10 transmits the path message or reservationmessage so as to promptly re-reserve the resources. The resourcereservation is classified into a receiver-initiated resource reservationand a sender-initiated resource reservation depending on which partstarts the resource reservation. The receiver-initiated resourcereservation is for the receiver to attempt to reserve the reservation.According to the receiver-initiated resource reservation, the resourcereservation is made in a manner that the sender transmits the pathmessage to the receiver, the receiver transmits the correspondingreservation message to the sender, and then the sender transmits anacknowledgement (ACK) message, for confirming the receipt of thereservation message, to the receiver. The ACK message is optional. Bycontrast, according to the sender-initiated resource reservation, theresource reservation is made in a manner that the sender transmits thereservation message to the receiver, and the receiver transmits the ACKmessage for confirming the receipt of the reservation message to thesender.

According to an exemplary embodiment of the present invention, bysetting specified refresh bits using a field that is not used among aheader part of the path message or reservation message, the localizedresource reservation can be attempted.

Specifically, if the mobile node 1 is the sender, the refresh bits areprovided on the header part of the resource reservation messageirrespective of the resource reservation type. For example, the pathmessage may be used in the receiver-initiated resource reservation, andthe reservation message may be used in the sender-initiated resourcereservation.

The refresh bits are provided on a flag field or reserved field partthat is not in use in the header. The refresh bits are composed of apre-reservation bit (hereinafter, referred to as the ‘P’ bit) forreporting the pre-reservation of resources, or a mobility bit(hereinafter, referred to as the ‘M’ bit) for reporting the completionof movement.

FIG. 6 illustrates refresh bits included in a header part of a resourcereservation message. Referring to FIG. 6, in the flag field of theheader, the ‘P’ bit and ‘M’ bit are set, with the ‘P’ bit and ‘M’ bithaving a specified bit size. ‘P’ bit refers to a part of the header thatcontains information on an instruction to pre-reserve resources and areservation limit time for refreshing a state of the pre-reservation ofresources, and ‘M’ bit refers to a part of the header for setting aninstruction to re-reserve resources by recognizing the termination ofthe handover and a refresh time value of the access network that issmaller than a refresh time value of the core network. The ‘M’ bit partis set for a prompt re-reservation of resources if the pre-reservationof resources fails, which will be explained below.

If the candidate access routers AR2 to AR4 receive the path message orthe reservation message from the present access router AR1, they set the‘P’ bit value among the refresh bits of the header part to ‘1’. Thecandidate crossover routers CR1 and CR2, found corresponding to thecandidate access routers AR2 to AR4, confirm the header part of themessages received from the candidate access routers AR2 to AR4. If the‘P’ bit value is ‘1’, they recognize it as a localized pre-reservationinstruction, that is, an instruction to reserve only resources betweenthe crossover routers and the candidate access routers, before thecompletion of the handover, and pre-reserve the corresponding resources.

If the mobile node 10 is the sender, in following the receiver-initiatedresource reservation, the mobile node 10 transmits the path message tothe respective candidate crossover routers CR1 and CR2, through thesearched candidate access routers AR2 to AR4. The respective candidatecrossover routers CR1 and CR2 confirm the ‘P’ bit of the header part ofthe path message. If the ‘P’ bit is set to ‘1’, they recognize this as aresource pre-reservation instruction, and establish the localizedresource reservation paths with the respective candidate access routersAR2 to AR4.

If the mobile node 10 is the sender, in following the sender-initiatedresource reservation, the mobile node 10 transmits the reservationmessage to the respective candidate crossover routers CR1 and CR2,through the candidate access routers Ar2 to AR4. The respectivecandidate crossover routers CR1 and CR2 confirm a resourcepre-reservation instruction from the refresh bits included in the headerpart of the reservation message, and make the localized resourcereservation with the respective candidate access routers AR2 to AR4.

Accordingly, irrespective of the receiver-initiated or sender-initiatedresource reservation, paths are pre-reserved through the respectivecandidate access routers AR2 to AR4, to which the mobile node 10possibly performs a handover with, and thus QoS can be secured even ifthe mobile node performs the handover to any access router.

If the mobile node 10 performs the handover to AR3, among the candidateaccess routers AR2 to AR4, AR3 becomes the new access router NAR and CR1becomes the crossover router. Accordingly, the mobile node 10 performscommunications with the correspondent node 20 using the path establishedthrough AR2. Thus, it is not required for other candidate access routersAR2 and AR4 to continuously keep the resource reservation state.Accordingly, in the ‘P’ bit, a specified refresh time value, that is, areservation limit time value optimized to match the handover situation,is set. If the pre-reservation state is kept over the reservation limittime, the corresponding resources are refreshed to reduce theunnecessary waste of resources. Specifically, if the resourcepre-reservation state is kept over the refresh time, the resourcereservation is re-performed by refreshing the resource reservationstate.

If the crossover router receives a binding update message after thecompletion of the handover, the crossover router immediately releasesthe existing resources, which are not in use and established in the oldaccess router, by transmitting a teardown message to the old accessrouter.

However, if the resource pre-reservation fails due to an absence ofuseful resources that can be supported by the RSVP router or due to thefailure of the RSVP router, the candidate sender nodes continuouslyattempt the resource pre-reservation until they receive the bindingupdate message (hereinafter, refer to as ‘BU message’) from the mobilenode. In the mobile IPv4/v6 environment, the mobile node 10 has a CoA(Care of Address) that is recorded in a home agent or the correspondentnode and reports the present position of the mobile node 10, and the CoAshould be updated whenever the mobile node changes its position. Bytransmitting the BU message, the mobile node can keep the connectionwith the correspondent node 20 or the home agent. That is, if thehandover of the mobile node 10 is completed, the mobile node 10transmits the BU message containing the present position information tothe candidate sender nodes.

The candidate sender nodes may be the candidate crossover routers,candidate access routers, or routers between the candidate crossoverrouters and the candidate access routers. These candidate sender nodessearch the nodes and routers that have useful resources until the BUmessage is transmitted from the mobile node. However, if the BU messageis received in a state that the resource pre-reservation has not beenfinally established, the candidate sender nodes attempt a promptre-reservation of resources. In attempting the re-reservation, there isa difference between the receiver-initiated resource reservation and thesender-initiated resource reservation.

According to the receiver-initiated resource reservation, if the senderrecognizes the failure of the resource pre-reservation, the senderattempts establishment of a path state. If the crossover router CR1 isthe sender, CR1 establishes the path state by sending the path messageto the new access router NAR. This can be achieved through the RSVProuters' recognition of the ‘P’ bit being set in the refresh bits. Sincethe new access router NAR recognizes the ‘P’ bit, the new access routerNAR keeps the path state without transmitting an error message (that is,a message for notifying that the NAR cannot continue to transfer thepath message to the final node) to the crossover router CR1 even the newaccess router NAR cannot transmit the path message to the mobile node 10until it receives the BU message. The path state denotes the state whererespective routers on the new path, through the new access router NAR,store the session information about the existing path. Accordingly, ifthe BU message is received from the mobile node 10, after the path stateis established, the NAR transmits the path message to the mobile node10, and thus a prompt resource reservation becomes possible.

If the path message is received, the mobile node 10 transmits thereservation message to the NAR. The NAR sets the ‘M’ bit among therefresh bits included in the header part of the reservation message. Thecrossover router CR1 establishes the localized path with the mobile node10, without transmitting the reservation message to the next RSVProuter, by recognizing the ‘M’ bit. Accordingly, the waste of resourcescan be prevented, and prompt resource re-establishment becomes possible.FIG. 6 illustrates the header part of the message that includes the ‘M’bit. Referring to FIG. 6, the resource pre-reservation is instructed bysetting the ‘P’ bit when the handover is in progress, and a promptresource re-reservation is instructed by setting the ‘M’ bit when thehandover is completed. The refresh time value of the access network maybe set to a value that is smaller than the refresh time value of thecore network using the ‘M’ bit. Since the reserved resources arerefreshed if the resource reservation state is maintained over therefresh time value, the refresh can be performed more frequently,compared to when the refresh is performed utilizing the refresh timevalue of the core network, and thus the unnecessary waste of resourcescan be prevented.

In the sender-initiated reservation, the candidate nodes (that is, nodesof the candidate access routers and the candidate crossover routers) canstore the state information for resource reservation by identifying the‘P’ bit of the reservation message received from the mobile node 10during the process of attempting the resource pre-reservation. If thehandover is completed, the mobile node 10 transmits the reservationmessage, where the ‘P’ bit is set instead of the ‘M’ bit, to thecrossover router CR1 through the new access router NAR. The crossoverrouter reports a ‘resource reservation success’ by transmitting theconfirmation message to the access router without transmitting thereservation message to the next RSVP router, by identifying the ‘M’ bit.The crossover router confirms the previously stored resource reservationinformation, and thus a prompt resource reservation can be made.

If the resource reservation succeeds through the receiver-initiated orsender-initiated resource reservation, the crossover router CR1 attemptsthe teardown of the existing resources established in the old accessrouter AR1.

FIG. 7 illustrates a process of releasing the existing resources.Referring to FIG. 7, the crossover router CR1 immediately releasesresources that are not in use by transmitting a teardown message to theold access router AR1.

FIG. 8 is a flowchart of a method for searching a crossover router if ahandover of a mobile node 10 occurs in an access network, according toan exemplary embodiment of the present invention. Referring to FIG. 8,if the mobile node 10 performs a handover from the old access router OARto a new access router NAR, the new access router NAR transmits the pathmessage (when the mobile node is the receiver) or a crossover router(CR) search message (when the mobile node is the sender) to a routerpositioned in an upper direction on a new path, in operation S810.

This message includes a session ID, a flow ID and a mobility object. Theupper router, which has received the message, confirms the session ID inthe message, and determines whether the session ID in the messagecoincides with the previously reserved session ID by comparing thesession Ids, in operation S820. If the session IDs do not coincide witheach other, in operation S830, the upper router determines that thesession has not been reserved in the present router and transmits thepath message or the CR search message to a new upper router or anadjacent router on the path in the direction of the correspondent node20, in operation S860.

In order to simply the search for the crossover router, the upper routercan search for the crossover router by comparing the IP logicalinterface number of the router which receives the message with the IPlogical interface number already stored in the router when the sessionIDs are identical with each other, in operation S840. Specifically, ifthe crossover router is positioned at a merging point of the old pathand the new path, the input logical interfaces of the messages receivedthrough the paths become different, and thus the crossover router cansimply be recognized by confirming the IP logical interface number. Ifthe IP logical interface numbers are different, the router confirmswhether the handover, has been re-performed through the confirming ofthe mobility object, in operation S870.

If the router positioned at the merging point cannot support the RSVPfunction, the corresponding router transmits the message to anotherupper router. The corresponding routers are positioned on the commonpath, and thus have the same IP logical interface number. Accordingly,the upper router positioned on the common path recognizes the crossoverrouter by confirming the flow ID of the received message. Specifically,if it is determined that the corresponding routers have the same IPlogical interface number, in operation S840, the upper router confirmswhether the existing flow ID is the same as the presently received flowID, in operation S850. If the flow IDs are also the same, the upperrouter confirms the mobility of the mobile terminal by confirming themobility object, in operation S860.

If the IP logical interface numbers or the flow IDs are different, thecorresponding router confirms whether the ‘H’ bit of the mobility objectin the path message or the CR search message are set to ‘1’, inoperation S870. The confirmation of the ‘H’ bit of the mobility objectis optional. If it is set to ‘1’, this represents that a handover hasoccurred, and thus the corresponding router confirms that it is thecrossover router. If the corresponding router cannot support the RSVPfunction, even though the IP logical interface numbers or the flow IDsare different, the corresponding router cannot perform the function of acrossover router, and thus re-searches for a crossover router amongupper routers.

If the crossover router fails, just after the search, another crossoverrouter should be re-searched by performing the above-described DPDprocess. If the crossover router fails after the resource re-reservationor the release of the existing resources is performed, the failurerepresents that the handover has already been terminated, and it is notrequired to re-search the crossover router. The corresponding router canconfirm whether the received message is an effective message bytransmitting a search message that includes the cookie.

By searching for the crossover router CR, as described above, the newaccess router NAR and the resources can promptly be re-reserved throughthe crossover router CR, and resources established with the old accessrouter are immediately released.

The crossover router CR upgrades the resource reservation state bytransmitting the path message, which has been transmitted to thecrossover router, to an upper router in the direction of thecorrespondent node 20, and discards the CR search message, in operationS880. By setting the ‘H’ bit of the mobility object in the path messageto ‘0’, the upper router is prevented from recognizing itself as thecrossover router.

FIG. 9 is a flowchart of the pre-reservation and re-reservation ofresources in a resource reservation system of a mobile network,according to an exemplary embodiment of the present invention. Referringto FIG. 9, if the handover of the mobile node 10 starts, in operationS910, the mobile node 10 transmits a handover start message forinforming the old access router OAR of the handover, in operation S915.As shown in FIG. 4, AR1 becomes the old access router OAR. As describedabove, the handover start message may include a mobility specificationthat contains mobility information of the mobile node and informationabout adjacent access routers. The mobile node 10 may report theoccurrence of the handover by setting the ‘H’ bit in the path message orthe reservation message to ‘1’ without separately transmitting thehandover start message.

If the old access router recognizes the start of the mobile node'shandover, the old access router searches the candidate access routersusing the session information included in the received message, inoperation S921. The old access router OAR can search access routers inan area, where the mobile node may possibly move, using a CARD algorithmfor searching the candidate access routers. As illustrated in FIG. 4,AR2 to AR4 may be the candidate access routers.

If the candidate access routers are searched, the old access router OARtransmits the session information to the respective candidate accessrouters, in operation S923. This session information may be included inthe path message or in the reservation message for refreshing theresource reservation established on the existing path, and transmittedto the candidate access routers.

The candidate access router CAR, which has received the sessioninformation, searches for a crossover router, that is, a candidatecrossover router, among routers positioned on the path in the directionof the correspondent node 20 using the session ID, flow ID and mobilityobject included in the information, in operation S925. The method forsearching the candidate crossover routers, according to an embodiment ofthe present invention is illustrated in FIG. 8. Specifically, thecandidate access router transmits the path message or the CR message tothe upper router in the direction of the correspondent node 20, and theupper router recognizes whether itself will be considered the crossoverrouter by confirming the session ID, flow ID and mobility object in themessage. The upper router may recognize whether itself will beconsidered the crossover router by confirming the logical interfacenumber.

If the crossover router is searched for, as described above, thecandidate access router instructs the crossover router to perform theresource pre-reservation before the handover is terminated by settingthe refresh bits in the header part of the path message (that the mobilenode is the sender) or the reservation message (when the mobile node isthe receiver). In the description, a message related to the resourcereservation, such as the path message or the reservation message, iscalled a resource reservation message.

As shown in FIG. 6, the refresh bits can include the ‘P’ bit and the ‘M’bit. If the candidate access router sets the ‘P’ bit value to ‘1’ andtransmits the bit value to the candidate crossover router, the candidatecrossover router recognizes this as the localized pre-reservationinstruction, in operation S930.

Accordingly, by changing the path message and the reservation message(for the receiver-initiated resource reservation) or by changing thereservation message and the confirmation message (for thesender-initiated resource reservation), the candidate crossover routerperforms the pre-reservation work, in operation S940. If the candidatecrossover router confirms that the ‘P’ bit value of the refresh bits,included in the resource reservation message, is ‘1’, the candidatecrossover router ceases to transmit the received resource reservationmessage to the router in the direction of the correspondent node 20.Accordingly, the localized pre-reservation can be performed.

The above-described pre-reservation work is continuously performedbefore the handover is terminated, in operation S950. If thepre-reservation is not performed until the handover is terminated, inoperation S951, the candidate access router establishes the path statefor a prompt re-reservation of resources, in operation S953. The pathstate represents the state of whether, if the binding update message ofthe mobile node is received, the path message can be immediatelytransmitted. For example, if the crossover router is the sender in thereceiver-initiated resource reservation, the crossover routerestablishes the path state by sending the path message to the candidateaccess router (that is, a new access router). This can be performedthrough the RSVP routers' identification of the ‘P’ bit set in therefresh bits. Specifically, the candidate access router recognizes the‘P’ bit, and thus keeps the path state without transmitting an errormessage (that is, a message indicating that the NAR cannot continue totransfer the path message to the final node) to the crossover router CR1even if it cannot transmit the path message to the mobile node 10 untilit receives the BU message.

If the handover is kept for more than a predetermined time after theresource pre-reservation has been successfully performed, the continuousmaintaining of this resource pre-reservation state may cause resourcesto be wasted. In order to prevent this, a refresh time value, that is, areservation limit time, is additionally set using the ‘P’ bit, and theresource reservation state may be refreshed if the established resourcereservation state is kept over the reservation limit time.

Specifically, the router determines whether the handover has beencompleted, in operation S955, in a state where the resourcepre-reservation has succeeded or the path state has been established.Then, the router determines whether the resource pre-reservation stateis continuously maintained over the reservation limit time set by the‘P’ bit, in operation S957, before the handover is completed. If it isdetermined that the resource pre-reservation state ha been maintainedover the reservation limit time, the router re-performs the resourcereservation work by refreshing the present state, in operation S959. Asdescribed above, the reservation limit time can be set to an optimizedvalue according to the mobility of the mobile node using the ‘P’ bit ofthe refresh bits. The candidate crossover router recognizes the ‘P’ bit,and locally reserves resources only between the candidate crossoverrouter and the candidate access router.

If the handover is completed, the mobile node transmits the bindingupdate message to a new access router, in operation S960. As describedabove, the binding update message represents a message by which themobile node informs a home agent HA and the correspondent node CN of itsown CoA. Through the binding update message, the candidate access routerrecognizes the completion of the handover by confirming the change ofCoA.

The candidate access router, which has received the BU message, sets the‘M’ bit instead of the ‘P’ bit, in operation S970. If the resourcepre-reservation is not performed, a prompt resource re-reservationshould be made, and thus the candidate access router reports thecompletion of the handover to the candidate crossover router through the‘M’ bit when the resource pre-reservation is not performed. According tothe setting state of the ‘M’ bit, the candidate crossover routerdetermines whether the resource pre-reservation has succeeded, inoperation S981. If it successful, the candidate crossover routerimmediately releases resources established in the existing accessrouter, in operation S990.

If the resource pre-reservation fails, the resource reservation betweenthe new access router and the new crossover router is promptlyestablished, in operation S983. Specifically, in the receiver-initiatedresource reservation, the new access router transmits the path messageto the mobile node 10, and the mobile node transmits the correspondingreservation message to the new crossover router through the new accessrouter. The crossover router receives this, and reestablishes resourcesbetween the new crossover router and the new access router, withoutcontinuing to transmit the resource establishment instruction to theother routers, by recognizing the ‘M’ bit.

If resources are reestablished, the crossover router releases resourcesestablished in the existing access router in the same manner as when thepre-reservation is made in operation S990. That is, by transmitting ateardown message to the existing access router, the crossover routerreleases the resource establishment.

In the sender-initiated resource reservation, the resources arere-reserved by exchanging the reservation message and the confirmationmessage. Even in the resource re-reservation as described above, theresource reservation is established only between the candidate crossoverrouter and the candidate access router by recognizing the ‘M’ bit. Aprompt refresh may be made by setting the refresh time value of theaccess network smaller than the refresh time value of the core network.

FIGS. 10 and 11 illustrate processes of performing the resourcepre-reservation and re-reservation, according to an exemplary embodimentof the present invention.

FIG. 10 illustrates a QoS signaling operation for a resourcepre-reservation when a mobile node performs a handover in the resourcereservation system, according to an exemplary embodiment of the presentinvention. Referring to FIG. 10, if the handover of the mobile node MNstarts, the handover start message is transmitted to the old accessrouter OAR. If the OAR receives the handover start message, a candidateaccess router search (CARD), a context transfer (CT), and a candidatecrossover router search (CCRD) are performed. The candidate crossoverrouters can be searched according to the flowchart of FIG. 8.

If the path message and the reservation message are exchanged betweenthe searched candidate crossover routers and candidate crossoverrouters, the resource pre-reservation is made, a new RSVP session isestablished between the mobile node MN and the new crossover router, andthe existing RSVP session is kept as it is between MAP and thecommunication correspondent node CN in the new crossover router.

If the resource pre-reservation is performed, the crossover routerreleases the resource establishment by transmitting a teardown messageto the existing access router OAR.

FIG. 11 illustrates a QoS signaling operation for a resourcere-reservation when the resource pre-reservation fails. If the resourcepre-reservation fails, the candidate access router keeps the path statewithout transmitting the received path message to the mobile node MN. Ifthe handover is completed and the BU is transmitted, the candidateaccess router becomes a new access router and transmits the path messageto the mobile node MN. The mobile node transmits the resourcereservation message to the candidate crossover router through thecandidate access router. Accordingly, a new RSVP session is establishedbetween the mobile node MN and the new crossover router, and theexisting RSVP session is kept as it is between MAP and the communicationcorrespondent node CN in the new crossover router. As described above,this process is performed using the ‘P’ bit and the ‘M’ bit included inthe refresh bits.

As described above, according to an exemplary embodiment of the presentinvention, a new RSVP path can be established in the access networkwithout establishing the end-to-end RSVP path, and thus the load ofintermediate routers in the core network can be reduced. Also, bysecuring the resources through a pre-reservation and a promptre-reservation, deterioration of QoS during a handoff operation can bereduced with a QoS setup delay also reduced.

Although the resources are pre-reserved, excessive resource reservationscan be prevented by properly adjusting a refresh time value, and ablocking probability, due to a double reservation of resources, can bereduced by promptly releasing existing resources. The system, accordingto an exemplary embodiment of the present invention, can especiallyoperate without requiring the addition of a proxy, and use an existingsystem without great modification since it uses fields that are not usedin the existing resource reservation message. Also, the presentinvention can be applied to both the receiver-initiated resourcereservation and the sender-initiated resource reservation. For a promptresource reservation, the present invention also provides a crossoverrouter searching method. Accordingly, duplication of resources can beprevented through the establishment of a localized path with a newaccess router after the crossover router is promptly searched.

Embodiments of the present invention may be implemented as a method,apparatus, system, etc. When implemented in software or computerreadable code, elements of the present invention can essentially be codesegments performing necessary tasks. The computer readable codesegments, or a program, can be stored/handled in/by a processor readablemedium or transmitted as computer data signals coupled to a carrier wavethrough a communication medium or network, for example. The processorreadable medium can include any medium that can store or transferinformation. Examples of the processor readable medium include anelectronic circuit, a semiconductor memory device, a ROM, a flashmemory, an erasable ROM (EROM), a floppy diskette, a CD-ROM, an opticaldisk, a hard disk, an optical fiber medium, an RF network, etc. Examplesof the computer data signals of the computer readable code include anysignals that can be transmitted through a transmission medium such as anelectronic network channel, an optical fiber, air, an electromagneticnetwork, and an RF network.

The foregoing embodiments and advantages are merely exemplary and shouldnot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Also, thedescription of the embodiments of the present invention is intended tobe illustrative, and not to limit the scope of the claims, and manyalternatives, modifications, and variations will be apparent to thoseskilled in the art.

Thus, although a few embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method for searching for a crossover router in a mobile networkhaving a mobile node, a correspondent node communicating with the mobilenode through a specified network, a first access router enabling themobile node to access the specified network, a second access routeraccepting the mobile node after being handed over from the first accessrouter, and a crossover router for establishing a new path through thesecond access router, comprising: an adjacent router positioned in adirection of the correspondent node on the new path, receiving a messageincluding session information, and comparing the session ID of thesession information included in the received message with a currentlyreserved session ID; comparing an interface through which the message isreceived with a pre-stored interface if the session ID and the reservedsession ID are identical; and recognizing the adjacent router as thecrossover router when it is confirmed from the received message that ahandover of the mobile node occurs, if the pre-stored interface and theinterface are not identical.
 2. The method as claimed in claim 1,further comprising: the adjacent router comparing a message flow IDincluded in the message with an existing flow ID if the pre-storedinterface and the interface are identical; and recognizing the adjacentrouter as the crossover router when it is confirmed from the receivedmessage that the handover of the mobile node occurs, if the existingflow ID and the message flow ID are not identical.
 3. The method asclaimed in claim 1, wherein the adjacent router comparing of the sessionID comprises the adjacent router transmitting the message to a router inthe direction of the correspondent node if the message session ID andthe currently reserved session ID are not identical.
 4. The method asclaimed in claim 3, further comprising: confirming whether the adjacentrouter, which is recognized as the crossover router, can perform acommunication normal operation with the mobile node and thecorrespondent node; and searching for another crossover router amongadjacent routers on the new path formed through a routing protocol if itis confirmed that the adjacent router is in a failure state and cannotperform the normal communication operation.
 5. The method as claimed inclaim 4, wherein the confirming of whether the adjacent router canperform the normal operation comprises: an old router of the crossoverrouter on the new path transmitting a specified search message to thecrossover router; and recognizing that the crossover router is in thefailure state if a confirmation message of the specified search messageis not received in a specified time from the crossover router.
 6. Themethod as claimed in claim 5, wherein the recognizing that the crossoverrouter is in the failure state further comprises: transmitting theconfirmation message, from the crossover router, with a cookie ofspecified contents; and the old router confirming whether theconfirmation message is an effective message by checking the cookie. 7.A mobile network comprising a plurality of access routers forcommunicating between a mobile node and a correspondent node, through atleast one of the plurality of access routers by implementing the methodof claim
 1. 8. A medium comprising computer readable code implementingthe method of claim 1.